Many electrically-powered assemblies and devices, such as luminaire assemblies, are hung from ceilings or other supporting structures. In order for a luminaire assembly to be hung, the weight of the luminaire assembly must be supported from the supporting structure. In addition, in order to provide light, the luminaire assembly must be provided with power.
Many kinds of supports have been developed to hang luminaire assemblies and to provide them with power. One form of support is an electrical cable configured to provide both power and support to the luminaire assembly. However, electrical cables composed of highly electrical metallic conductors can only suspend luminaires up to approximately 5 pounds. When an electrical cable needs to support more than 5 pounds, a separate suspension or support cable is required, and the electrical cable will require an insulating jacket of a non-metallic material such as a polymer or elastomer.
The use of non-metallic insulators with metallic conductive cables can cause a number of problems with the use of adjustable cable grippers. Specifically, adjustable cable grippers need to come into direct contact with the metallic cable to be effective. When a cable gripper is used on a non-metallically insulated cable it will slip and tear the insulation, eventually lodging against the metal itself and defeating the purpose of the insulation.
The use of mixed strands of metallic cable for both supporting light assemblies and conducting electricity thereto are known. Several attempts to meet the goal of adequate support and strength in the cable, while still providing adequate conductivity are shown in the prior art. However, these attempts do not cure the problems with the use of adjustable grippers.
Several examples from the prior art disclose cables which use a combination of cooper wires and steel wires. Some of those examples depict steel wires and copper wires exposed on the outer layer of the cable. U.S. Pat. No. 2,250,907, issued to Edwards, and U.S. Pat. No. 3,339,012, issued to Hutchins, depict some of those cables. While copper has good electrical conductivity, copper also has a low elastic strength. The presence of the copper on the outer later of the cable means that the exterior of the cable lacks the lateral compression strength required for the cable to be gripped with adjustable grippers.
Other examples in the prior art depict the steel wires on the outer layer of a cable, but those cables are not configured to be gripped by adjustable grippers. U.S. Pat. No. 2,396,734, issued to Williams, and U.S. Patent Application Publication No. 2001/0000590, applied for by Valadez et al, depict some of those cables.
Other examples in the prior art use alternative metallic materials to provide both conduction and tensile strength. However, those alternative metallic materials lack the lateral compressive strength for use with adjustable grippers. U.S. Pat. No. 3,261,908, issued to Roche et al, and U.S. Patent Application Publication No. 2001/0017219, depict some of those cables.
Yet other examples in the prior art require non-metallic insulation which, as discussed above, is destroyed which gripped by an adjustable gripper. U.S. Pat. No. 7,462,781, and U.S. Patent Application Publication No. 2005/0109530, applied for by Maeda, depict some of those cables.
While all of these prior art cables use metallic strands to provide tensile strength for the cable, the prior art cables fail to disclose a cable with sufficient lateral compression strength to be gripped with an adjustable gripper, configured to be gripped by an adjustable gripper, and without the use of a polymer or elastomer insulation. The prior art fails to disclose the outer steel strands as providing protection to the internal conductive strand against the lateral compression forces of an adjustable cable gripping mechanism such as a three-ball compression system.
What is needed in the area of supporting luminaires and other electrical equipment is a conductive cable providing both axial tensile strength and resistance to lateral compression forces that is needed to support a hanging luminaire assembly or other electrical equipment using an adjustable cable gripper.